Conventionally, a coating film is formed on a surface of an article of glass, resin or the like for various purposes. As the method of forming the coating film, for example, there is a known method of forming a silicon oxide-based cured coating film by the sol-gel method under mild conditions utilizing a hydrolysis and condensation reaction of a hydrolyzable silicon compound. According to this method, generally, a liquid composition containing a hydrolyzable silicon compound and a catalyst such as acid is prepared, and this is applied on the surface of the article and heated and cured to form a coating film.
A problem in such a silicon oxide-based cured coating film is that when a large amount of a tetrafunctional hydrolyzable silicon compound is used to increase the hardness, cracks and the like occur in the coating film to be obtained. In order to solve the problem, an organic compound is added as a flexibility-imparting component so as to improve the film-forming property. Further, to impart various functions, for example, ultraviolet absorbency and infrared blocking property to the coating film, organic dye or inorganic particles having these functions are often blended (refer to, for example, Patent Reference 1 (International Publication No. WO2010/131744)).
Here, the above liquid composition containing the hydrolyzable silicon compound has problems in storage stability such as polymerization of the silicon compound because hydrolysis gradually proceeds during long-term storage and the like. Hence, it is known that keeping the pH low in a state of the liquid composition improves the storage stability. In a liquid composition with a low pH, however, when containing the above various organic compounds, inorganic particles and the like, there is a problem that the durability such as alkali resistance decreases in the cured coating film obtained after long-term storage, and the problem is prominent when the curing temperature is relatively low.